The COMB Limiter Combiner (CLIC) described in U.S. Pat. No. 6,549,560 to Maiuzzo et al. prevents strong interfering signals in nearby frequencies from overloading the amplifier and limiter stages in the front end of communications receivers. CLIC operates by, in part, restricting inter-modulation products to the passband of a single bandpass filter. CLIC design has generally been limited to between 10 and 16 channels due to the effect of each CLIC channel on the performance of the other CLIC channels, as well as the increased difficulty in electrically aligning an increased number of CLIC channels.
For many applications, it is desirable to have a filtering device that can achieve the same performance as CLIC, while operating over a broad frequency range. As an example, consider the application of CLIC to the military UHF band of 225 MHz to 400 MHz. The Electromagnetic Compatibility (EMC) goal is specified in terms of the acceptable adjacent signal separation, which is the specified separation required between a receive signal and all co-site transmit signals. For the military UHF bands, the adjacent signal separation is usually 1 MHz to 5 MHz. Therefore, 35 CLIC sub-bands would be required for an adjacent signal separation of 5 MHz, while an adjacent signal separation of 1 MHz would require 175 CLIC sub-bands. Such amounts of sub-bands are not feasible given the limitations in CLIC design as discussed above.
A need exists for a filtering device that can achieve the same performance as CLIC, i.e. minimizing intermodulation and mitigating potential interfering signals, but includes significantly more channels to allow operation over a broad frequency range.